The invention relates to mobile communication systems, and more particularly to methods and apparatuses for efficiently accumulating and storing trace log information related to user sessions.
Performance management is an important aspect of mobile communication system operations. Performance management includes, but is not limited to, monitoring the performance of end-user services, network elements and the like; identifying bottlenecks in the system, and taking appropriate actions to battle poor quality.
With the advent of new systems, the addition of more services, and a more diverse terminal population, performance management is getting increased attention within the industry.
The existing technology for performance management in systems like the Global System for Mobile communication (GSM) and Wideband Code Division Multiple Access/High-Speed Packet Access (WCDMA/HSPA) uses a combination of counters and trace functions.
In performance management there is an inherent tradeoff between the granularity (or resolution) of the performance information to be collected and the amount of performance management related data that needs to be sent from a node (e.g. a radio base station). The more information collected, the better system performance can be managed. However, storing and communicating this greater amount of information from its collection point (e.g., a radio base station) to a performance management node requires a correspondingly greater amount of system resources, which has the undesirable effect of degrading system performance.
Counters have the lowest resolution in that they aggregate a lot of information into a single number (e.g., total number of dropped calls in a cell). By contrast, tracing functions have the highest resolution in that a large amount of information about a single user equipment (UE) is recorded and sent to the performance management system. In contrast to count information, a tracing function can capture such things as when and why a UE dropped its calls. The drawback is the amount of information that needs to be communicated from the traffic node to the performance management system (very often called an Operations and Maintenance, or “O&M” system). Moreover trace functions scale with the number of users (i.e., tracing N users requires N times more information than tracing one user) so that, given the limitations of conventional trace management techniques, only a small fraction of the terminals can be traced at any one time.
FIGS. 1a-1d depict signaling and events related to the management of trace log information in an exemplary mobile communication system 100 having a management system 101 (e.g., Operations System Support—“OSS”), a core network node 103 (e.g., Mobility Management Entity—“MME”), and first, second and third radio base stations 105, 107, 109 (e.g., eNodeBs). Communications between each of the first, second and third radio base stations 105, 107, 109 and the core network node 103 take place by means of respective S1 interfaces. Communications between each of the first, second, and third radio base stations 105, 107, 109 and (at least) neighboring radio base stations take place by means of X2 interfaces. (In some systems, radio base stations can also communicate with one another by means of the S1 interfaces.) An exemplary UE 111 is depicted as being within a service area of the first radio base station 105.
Referring first to FIG. 1a, in an initiation aspect of UE tracing, the management system 101 sends a “trace start” command (step 151) to the core network node 103. The core network node 103 now knows that it should maintain a trace log of information relating to at least some UE sessions.
Next in this example, the UE 111 accesses the first radio base station 105 to initiate a session (step 152). The first radio base station, in turn, effectively forwards this message to the core network node 103 (step 153). It will be noted that the management system 101 may have instructed the core network node 103 to trace only specified UEs (e.g., based on the UE's International Mobile Subscriber Identity—“IMSI”) rather than all UEs. In this example, the UE 111 is to be traced, so the core network node 103, having found that the identifier (ID) of the UE 111 (contained in the message of step 153) indicates the same UE as a UE ID included in the message of step 151, instructs the first radio base station 105 to begin this tracing (step 154). The first radio base station 105 acts accordingly.
Referring now to FIG. 1b, at some point in time, a decision is made in the first radio base station 105 to hand over the UE 111 to the second radio base station 107. Accordingly, the first radio base station 105 sends a signal to the second radio base station 107 instructing the latter to assume responsibility for the UE session and to begin a trace process for the UE 111 (step 155). Assuming that the handover is accepted, this decision is communicated to the UE 111 (step 156). The UE 111 then accesses the second radio base station 107 (step 157).
Continuing the example with reference to FIG. 1c, at some point in time, a decision is made in the second radio base station 107 to hand over the UE 111 to the third radio base station 109. Accordingly, the second radio base station 107 sends a signal to the third radio base station 109 instructing the latter to assume responsibility for the UE session and to begin a trace process for the UE 111 (step 158). Assuming that the handover is accepted, this decision is communicated to the UE 111 (step 159). The UE 111 then accesses the third radio base station 109 (step 160).
To conclude the example, with reference now to FIG. 1d, at some point in time it is time to report the collected trace log information to a trace log storage node 113, which is also part of the mobile communication system 100 (e.g., within the management system 101 or located at another Internet Protocol (IP) address). This can be based, for example, on satisfaction of a session report criterion (e.g., termination of the UE session as depicted by step 161). Accordingly, each of the first, second, and third radio base stations 105, 107, 109 communicates the collected trace log information to the trace log storage node 113 (steps 162-1, 162-2, 162-3).
It will be apparent that the amount of data that is recorded, stored and transported in the conventional approach becomes quite large if the choice is made to activate such tracing for the entire network. The inventors have considered a number of different approaches for decreasing these logs:                1. Decrease the amount of information recorded for each event (i.e., decrease trace depth).        2. Limit the number of events that are recorded (e.g., skip recording handover related events if they are not considered interesting).        3. Only keep and upload the recorded files if the end of the session for the UE satisfied certain predefined session report criteria (e.g., only upload recorded trace log information if the UE session ended in an abnormal way, such as a dropped call). In all other circumstances, the recorded trace log files are not uploaded, and are deleted locally.        4. Alternative 3), and in addition further reduce the recording file size by only keeping the events recorded during the last X seconds. This feature is herein referred to as “Event History Buffer/Connection Drop Log”.        
The present inventors have recognized that a problem exists with the “Event History Buffer/Connection Drop Log” approach to trace log processing in that no mechanism has been provided for informing a radio base station (e.g., eNodeB) whether to keep the recorded files and upload them to the trace log storage 113 in the even that the UE has been handed over to another eNodeB. This is a problem because the source radio base station (i.e., the one from which the UE session was handed over to a target radio base station) has no information about how a session ended, and can therefore not determine whether the predefined session report criteria have been satisfied. Additionally, the source radio base station does not know how long the session lasted, and therefore has no way of determining whether any of the trace log information that it is maintaining was recorded during, e.g., the last X seconds.
It is therefore desirable to provide methods and apparatuses that more efficiently enable trace log information to be collected and supplied to a performance maintenance node in a mobile communications system.